The present invention is directed to a control device for controlling functions of a motor vehicle for a load dump. The device has a computer for generating at least one control signal that is dependent on the level of an operating voltage.
For example, such functions are the open time of an injection valve, the position of a throttle valve regulator and/or the charging time of an ignition coil. The length of the control signals controlling these units is dependent on the operating voltage applied to them in order to achieve a desired condition, such as quantity of fuel injected, position of the throttle valve or stored ignition energy, independently of the level of the operating voltage.
Since the operating voltage in a motor vehicle is supplied by a battery with a generator connected in parallel thereto and since the battery voltage can change only slowly, it has been sufficient for control devices with a computer to sense the operating voltage only from time to time and to base the calculation of the control signals on the value that was most recently sampled.
The present invention is based on the recognition that this procedure leads to unsatisfactory results under special operating conditions: namely, it can occur that the connection between the battery and generator is briefly or permanently broken. This then results in a significantly increased operating voltage for a sudden load dump whose size, among other things, is dependent on the speed of the generator (load dump). Since this operating situation is unpredictable but must be immediately taken into consideration, the computer would practically have to sense the operating voltage every millisecond. This, however, would result in a correspondingly costly design of the computer which however cannot be justified since the operating situations that have been described occur rarely.